Glaciology L6: Ice ages and past glacier extent

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What is the current total world coverage of ice?
14,898,320 km 2 (10% surface of the Earth)
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What is meant by the terms "icehouse" and "greenhouse"?
Icehouse- periods of greater than average glacier extent. Greenhouse= periods of little//no ice cover
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What is the current state of glacial extent?
Icehouse- large ice sheets are present @ the poles and mountain glaciers are widespread.
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When did the current icehouse start? Why?
34 ma BP global temperature fell from 22 oC - 12 0C
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What may have been the main cause of the three icehouse states prior to the current one?
When part of a supercontinent of landmasses (Gondwana) being located at the South Pole
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How was Gondwana formed?
When Pangea broke up around 200 ma BP - Gondwana huge southern section
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When did the two most severe icehouses occur?
2.3/2.2 ba BP and 740-630 ma BP
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What happened during these extreme icehouses?
Glaciers extended to near the equator. Global average temperature was
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What may have caused these extreme icehouse phases?
Significant changes in atmospheric oxygen concentrations- maybe related to evolution of life?
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What else can control the earth's surface temperature aside from the Milankovitch cycles?
Over billions of years- solar luminosity has increased - more short-wave infra red radiation reaches the Earth e.g. 4 ba BP- solar output was 75 % of its current value- explains why past climate was more susceptible to icehouse state
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What is the early faint sun paradox?
Despite solar insolation being < 75 % current value- liquid water has been present throughout Earth's history.
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What may be an answer to the early faint sun paradox?
Envelope of greenhouse gases e.g. CO2
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How does CO2 atmospheric concentration change over time?
Over 10s-100s ma: plate tectonic= important. This controls how much carbon is removed from the atmosphere as rock is weathered, products are buried in ocean sediments, then subducted @convergent plate margins. Carbon = released by volcanic activity
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How might tectonism favour icehouse/greenhouse conditions?
Low volcanic activity + supercontinent = low C02= icehouse; Many dispersed continents-rapid seafloor spreading=volcanism=high CO2: Greenhouse conditions
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How else might tectonism control whether an icehouse or greenhouse is prevalent?
Distribution of continents, mountains etc controls patterns of atmospheric/oceanic circulation (distribution of energy around the world effects the climate)
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How might tectonism have contributed towards the development of the current icehouse phase starting 34 ma BP?
Uplift of the Tibetan plateau, Himalaya and Cordillera (N&S America). Drake's passage (between S.America + Antarctica) deepened- Antarctic circumpolar current developed- less heat flux from lower latitudes
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What are glacials and interglacials?
Shorter term fluctuations in climate and ice cover extent that are superimposed on icehouse periods
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What is it believed is mostly responsible for the glacials and interglacials experienced over the last 2 ma BP?
Likely to be related to changes in the Earth's orbit around the sun- other factors involved though
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What is the name of the period starting 2 ma BP?
Quaternary
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Why do we have good knowledge of how climate has varied during the Quaternary (last 2 ma BP)?
Oxygen-isotope records e.g. in shells
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What is the name of the current icehouse?
Late Cenozoic glaciation
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How is it believed the current icehouse started?
Began in Antarctica- mountain glaciers coalesce into ice sheets and spread
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When was the N hemisphere glaciation initiated?
3.2 ma BP
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Which ice sheets have persisted/ retreated since?
Laurentide was the biggest- has not persisted Greenland- persisted through some interglacials
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When did the Eurasion ice sheet develop?
Developed several times during the quaternary. LGM- 20 ka BP. Equilibrium line altitudes (ELA's) of glaciers was 1000 m lower than today
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How is the past activity of the British isles ice sheet being investigated today?
Glaciers elsewhere are being observed using remote-sensing techniques e.g. Norway. - can produce models of potential behaviours of past sheets/glaciers
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How is it believed the british isles ice sheet changed over time?
Dynamic ice streaming system- repeat binge-purge cycles driven by internal instabilities and moderated by external climate forcing. Rapid deglaciation from maximum extent in less than 2,000 years ( 2 m sea level equivalent).
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Since the last glacial maximum has there been consistent deglaciation?
Nope. Lots of evidence of glacier oscillations over 100s-1000 year timescales. e.g. Younger Dryas/Loch Lomond Stadial (12,900-11,600 yrs BP). Significant cooling over Greenland-ice caps and glaciers in UK and Scandanavia (smaller readvances elsewhere
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What was the likely cause of the Younger Dryas period?
An outbursting of meltwater from a glacial lake: Agassiz - draining meltwater from the remains of the Laurentide ice sheet. Freshwater into Labrador sea- disrupted thermhaline circulation- reduced heat towards the poles.
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What is the problem with using the Agassiz outburst theory to explain the Younger Dryas glacial readvancement?
Some mismatch between the two events- but widely accepted
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What was the little ice age?
Biggest most recent cooling phase (although no glacial growth in UK). Starting in 13th Century- many mountain glaciers advanced worldwide.
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What caused the little ice age?
Maunder minimum- reduced solar activity- period of minimum sunspot activity coincides. Also- lots of volcanic activity- aerosols cause sunlight to be scattered back into space? (possible- more work on volcanic forcings needs to be done)
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In the pre-industrial era what were the most important controls on climate?
Solar and volcanic controls
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How have the levels of atmospheric C02, CH4 and NOx changed over time?
Now- levels unprecedented over at least the past 800,000 years (IPCC, 2013)
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How certain is it the changed greenhouse gas concentrations are impacting climate?
"Warming of the climate system is unequivocal" (IPCC, 2013)
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What is it agreed is likely to be the dominant cause of warming starting from the mid-20th century?
Human influence (IPCC, 2013)
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Card 2

Front

What is meant by the terms "icehouse" and "greenhouse"?

Back

Icehouse- periods of greater than average glacier extent. Greenhouse= periods of little//no ice cover

Card 3

Front

What is the current state of glacial extent?

Back

Preview of the front of card 3

Card 4

Front

When did the current icehouse start? Why?

Back

Preview of the front of card 4

Card 5

Front

What may have been the main cause of the three icehouse states prior to the current one?

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Preview of the front of card 5
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